Variants of physiological FDG vascular activity on digital PET.

Objective: Fluorodeoxyglucose PET/computed tomography (FDG PET/CT) is effective in detecting large vessel vasculitis. Digital PET cameras have improved spatial resolution compared with analog PET, resulting in more prominent physiological uptake in arterial walls. This study's goal was to define qualitative normal variants of arterial activity on digital PET/CT.

Methods: We retrospectively reviewed 126 oncological PET/CT studies. Exclusion criteria included history of vasculitis, immunosuppressant therapy, hyperglycemia, or altered FDG biodistribution. Qualitative vessel wall activity (common carotid, brachiocephalic, subclavian, aorta, and femoral) was visually graded by two nuclear physicians with guideline-proposed criteria: 0: ≤mediastinum, 1: liver, where grade 3 is compatible, 2 is possible, and <2 is negative for vasculitis. Cranial artery uptake was visually graded as follows: grade 0: ≤surrounding tissues, grade 1: just above surrounding tissues, and grade 2: significantly above surrounding tissues, with grades 1 and 2 considered positive for cranial artery vasculitis.

Results: Large vessel uptake was grade 3 in 0 subjects, grade 2 in four subjects (3%), grade 1 in 87 subjects (69%), and grade 0 in 35 subjects (28%). In studies acquired ≥75 min post-injection, 1/15 subjects had grade 2 uptake. Four subjects (3%) had grade 1 vertebral artery uptake. No subjects had temporal, maxillary, or occipital artery uptake.

Conclusion: A minority of our subjects presented with grade 2 large vessel uptake, which was associated with longer uptake times, or grade 1 cranial artery uptake, which was associated with higher age and glycemia. These findings should be interpreted with caution in patients referred for suspected vasculitis, as they may represent normal variants on digital PET.